Denitrification on internal carbon sources in RAS is limited by fibers in fecal waste of rainbow trout

doi:10.1016/j.aquaculture.2014.08.004

Aquaculture

Volume 434, 20 October 2014, Pages 264-271

https://doi.org/10.1016/j.aquaculture.2014.08.004 Get rights and content

Highlights

•
Denitrification reactors were operated with fecal waste as only COD source in RAS.
•
Denitrification removed 48% of the total nitrogen waste produced by the fish.
•
44% of the supplied fecal COD was degraded within the reactor.
•
45% of the degraded COD originated from cellulose and hemicellulose.

Abstract

Denitrification on internal carbon sources offers the advantage to control nitrate levels in recirculating aquaculture systems (RAS) by using the fecal carbon produced within the husbandry system. However, it is not clear to which extent fecal carbon can be utilized by the microbial community within a denitrification reactor. Especially fibers can hamper the bioavailability of carbon in fecal waste. Therefore, this study investigated the nitrogen removal capacity of a denitrification reactor using fecal waste with a high fiber content as the only carbon source in RAS. Furthermore, we investigated to which extent fibers were utilized as a carbon source within the reactor.

Four identical small-scale RAS (V = 460 L) were stocked with 25 rainbow trout of ~ 110 g, and operated at a water exchange rate of ~ 200 L/kg of feed DM. Two RAS served as controls without denitrification and two RAS were upgraded with an upflow sludge blanket denitrification reactor (V = 10.5 L). During the six weeks of experiment, we determined COD (chemical oxygen demand, measure for organic carbon) and N balances for all systems and analyzed the composition of the collected solids. The denitrification reactors were able to remove 19 g N/kg of feed DM, or 48% of the metabolic nitrogen waste produced by the fish. Based on the COD balances, 44% of the supplied fecal COD was degraded in the reactor. Hemicellulose and cellulose degradability was ~ 50%, accounting for 45% to the total degraded COD. Under steady state conditions, 4.4 g of biodegradable COD needed to be oxidized to reduce 1 g of nitrogen, indicating respiratory COD losses of approximately 50%.

This experiment successfully demonstrated that denitrification on internal carbon sources using a high fiber diet could remove half of the nitrogen waste produced by the fish. Although fibers limited carbon bioavailability, half of the cellulose and hemicellulose present in the fecal waste was utilized in the denitrification reactor.

Introduction

Recirculating aquaculture system (RAS) technology has been successfully adopted for the land-based production of salmon and trout, and the number of farms using RAS keeps on increasing (Martins et al., 2010). However, the use of RAS is often limited by the high energy demand of the systems, and by regulatory limitations on water intake and discharge. To resolve the bottleneck of water intake and discharge, nitrate levels in fish husbandry systems must be controlled. This is usually done by water refreshment, which will eventually determine the minimal water intake and discharge of a husbandry system (Timmons and Ebeling, 2007). Besides controlling nitrate levels in RAS by water refreshment, the accumulation of nitrate can also be counteracted by using denitrification reactors (Balderston and Sieburth, 1976). Denitrification is an anoxic microbial process using organic carbon to convert nitrate into nitrogen gas, generating CO₂ and alkalinity (Eq. (1)). Usually, external carbon sources like methanol or acetate are used to fuel a denitrification reactor (van Rijn et al., 2006).

Stoichiometry of denitrification, using methanol as a carbon source (Tchobanoglous et al., 2004):5 CH₃OH + 6 NO₃⁻ → 3 N₂ + 5 CO₂ + 7 H₂O + 6 OH⁻

Some systems even use the fecal waste, which is produced within the husbandry system, as the only carbon source for denitrification (Gelfand et al., 2003, Martins et al., 2010). The advantage of using fecal waste as an internal carbon source is the concurrent reduction of the solid waste stream, of which the further treatment and disposal is often a costly process. Thus, denitrification on internal carbon sources looks like an elegant solution to reduce the water demand and waste production in RAS (Martins et al., 2010, Van Rijn et al., 2006). However, the efficiency of denitrification on internal carbon sources is usually limited by the amount of carbon available for the microbial community within a denitrification reactor (Klas et al., 2006a).

Meriac et al. (2014) showed that the carbon bioavailability in fecal waste of fish was significantly reduced by fibers originating from unpurified plant ingredients in the feed. Fibers can only be used as a carbon source by the bacteria within a denitrification reactor after hydrolysis, which is considered the rate limiting step in the degradation of organic material (Hendriks and Zeeman, 2009, Noike et al., 1985). The question arises, to which extend fecal waste with a high fiber content can be utilized within a denitrification reactor. This will become a more important issue, considering the trend for an increased substitution of fish meal with plant-based ingredients (Naylor et al., 2009).

Therefore, we designed an experiment [i] to investigate the nitrogen removal capacity of a denitrification reactor using fecal waste with a high fiber content as the only carbon source, and [ii] to determine to which extend cellulose, hemicellulose and lignin in fecal waste can be utilized as a carbon source in denitrification.

Section snippets

Experimental design

Four identical RAS were used in this experiment, of which two served as control systems and two were upgraded with an upflow sludge blanket denitrification reactor. However, those four systems were part of a larger experiment, which was designed to investigate two independent research questions in a total of six RAS. The two remaining RAS were used to test a different hypothesis, and the obtained results are not included in this paper. The experiment was approved by the Ethics Commission for

Water quality, fish performance and system management

NO₂–N and NO₃–N levels were significantly lower in RAS with denitrification when compared to the control systems (p < 0.05, Table 4). At the end of the experiment, the average NO₃–N levels in denitrification systems were 100 mg/L against 160 mg/L in the control systems (Fig. 2). No significant differences in fish performance were observed between treatments (Table 5). Systems with denitrification consumed only 87 g of bicarbonate when compared to 211 g in the controls. Analysis of the fecal waste

Water quality and management

As expected, the denitrification reactors were able to control nitrate levels in the systems. Although literature suggests that incomplete denitrification can result in the additional production of nitrite (Balderston and Sieburth, 1976), we found higher nitrite concentrations in control systems when compared with the denitrification systems. This effect cannot be explained by a net removal of nitrite in the reactors, as the NO₂–N concentration in the reactor effluent was on average 0.6 ± 0.3 mg/L

Conclusions

We demonstrated successfully that an upflow-sludge blanket denitrification reactor was able to remove half of the nitrogen waste produced in RAS, by using fecal waste produced in the system as the only carbon source. Although fibers limited the bioavailability of carbon in the fecal waste, approximately half of the COD present in feces as hemicellulose and cellulose was utilized by the reactor. This study shows, that diet composition plays an integral role for the carbon budget for a

Acknowledgments

We would like to acknowledge Interreg IV A (IVA-VLANED-1.41) and Agentschap NL (IWA09022) for the funding and all contributors of the EM-MARES and AquaVlan project consortia.

References (24)

A.T.W.M. Hendriks et al.
Pretreatments to enhance the digestibility of lignocellulosic biomass
Bioresour. Technol.
(2009)
A.M. Henken et al.
A comparison between methods used to determine the energy content of feed, fish and faeces samples
Aquaculture
(1986)
S. Klas et al.
Conceptual, stoichiometry-based model for single-sludge denitrification in recirculating aquaculture systems
Aquaculture
(2006)
S. Klas et al.
Development of a single-sludge denitrification method for nitrate removal from RAS effluents: lab-scale results vs. model prediction
Aquaculture
(2006)
C.I.M. Martins et al.
New developments in recirculating aquaculture systems in Europe: a perspective on environmental sustainability
Aquac. Eng.
(2010)
A. Meriac et al.
Dietary carbohydrate composition can change waste production and biofilter load in recirculating aquaculture systems
Aquaculture
(2014)
K.I. Suhr et al.
End-of-pipe denitrification using RAS effluent waste streams: effect of C/N-ratio and hydraulic retention time
Aquac. Eng.
(2013)
Y. Sun et al.
Hydrolysis of lignocellulosic materials for ethanol production: a review
Bioresour. Technol.
(2002)
A. Tacon et al.
Comparison of chromic oxide, crude fibre, polyethylene and acid-insoluble ash as dietary markers for the estimation of apparent digestibility coefficients in rainbow trout
Aquaculture
(1984)
J. Van Rijn et al.
Anaerobic treatment of intensive fish culture effluents: digestion of fish feed and release of volatile fatty acids
Aquaculture
(1995)

J. Van Rijn et al.

Denitrification in recirculating systems: theory and applications

Aquac. Eng.

(2006)

M. Zhang et al.

Pyrolysis of lignin extracted from prairie cordgrass, aspen, and Kraft lignin by Py-GC/MS and TGA/FTIR

J. Anal. Appl. Pyrolysis

(2012)

Cited by (12)

Performance on horizontal flow and folded plate denitrification bioreactor recycling waste sawdust and municipal sludge for continuously treating simulated agricultural surface runoff
2021, Journal of Cleaner Production
Citation Excerpt :
Natural cellulose, hemicellulose and lignin are often used as natural solid carbon sources in denitrification bioreactors because they not only slowly release the carbon source for the survival of microorganisms, but also serve as carriers for the attachment of microorganisms (Feng et al., 2013). In previous studies, discarded newspaper (Boussaid et al., 1996), barley straw (Healy et al., 2011), five kinds of natural cellulose materials (reed leaf, cattail leaf, camphor leaf, pine branch and rice straw) (Li et al., 2013), fecal waste (Meriac et al., 2014), rice straw (Tao et al., 2019), industrial potato residues (Sepideh et al., 2020) and high-tannin oak woodchips (Wickramarathne et al., 2021)were used as solid carbon sources for denitrification bioreactor to remove nitrogen from wastewater. Only wood-particle products (e.g. woodchip and sawdust) is used as carbon source in denitrifying bioreactor, which can continuously produce carbon for 5–15 years to supply the survival of microorganisms (Schipper et al., 2010).
Nitrogen removal from agricultural surface runoff is of great significance to protect the water quality and safety of groundwater and drinking water. The denitrification bioreactor uses wood-particle products and municipal sludge as solid carbon sources to treat agricultural surface runoff and the rule of total nitrogen produced by wood-particle products is still blank. In this study, a type of denitrification bioreactor with municipal sludge (MS) and Cunninghamia lanceolata sawdust (CLS) as solid carbon source to denitrify simulated agricultural surface runoff is designed. Results show that CLS can release approximately 0.86 ± 0.06 mg L⁻¹ of nitrogen into the water, and the release process conforms to Non-Fickian transport (n = 0.46). The addition of MS is beneficial to increase the average degradation rate of NH₄⁺-N (70.94%). Increasing the inflow rate is beneficial to increase the average degradation rate of NO₂⁻-N, NO₃⁻-N and TN. When the influent flow is 1.34 mL min⁻¹, the average degradation rate of NO₂⁻-N is as high as 61.61% while of TN is 86.04% in the CLS horizontal flow denitrification bioreactor. The average degradation rate of NO₃⁻-N of CLS and MS (sludge-water volume ratio = 1:2) folded plate denitrification bioreactor is 95.72%, which is 17.46% higher than the horizontal flow type. Based on the principle of cleaner production, this study recycles waste CLS and MS as solid carbon sources in the bioreactor to continuously treat and simulate agricultural surface runoff. The device can not only degrade high-concentration nitrogen, but also prevent the generation of waste and waste of energy, which is a new surface runoff pollution control technology.
Emerging scope, technological up-scaling, challenges and governance of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) production in Himalayan region
2020, Aquaculture
Citation Excerpt :
The production of rainbow trout (Oncorhynchus mykiss Walbaum 1792) is practiced in different production systems which are mostly extensive system (ES), however, recirculating aquaculture systems (RAS) can be used for intensive trout production (Samuel-Fitwi et al., 2013). Since extensive trout production systems practiced in India is based on limited requirements of resource and hence subsequent output and emissions may not impact the environment (Meriac et al., 2014). Nevertheless, intensifying trout culture may possibly impact the environment besides adequate usage of water and resources as feed.
Rainbow trout is one of the promising cultivable fish species in coldwater and has enormous scope for its expansion in the Himalayan region. Being a low volume high value commodity, the trout has good potential for domestic consumptions as well as foreign export. In spite of having excellent positive traits and prosperity, the development and expansion of trout farming in Himalayas has yet to be intensified for large-scale productions. There are enormous aquatic resources in the form of river, reservoirs and lakes in the Himalayan region yet agricultural production of trout is very limited. This paper presents the available trout production system, available infrastructure and production trend highlighting the need of improved feed, infrastructure, improved strain, application of triploid trout production for stocking in cages and pens and also the possibilities of organic trout farming so as to clinch the production intensification, environmental management and trout promotion objectives. Based on 15 years experience of trout culture in India, potential success in trout production could be acquired through technological modernization, better governance and significant improvement in the management practices. The knowledge needed to form a comprehensive trout-farming ecosystem beyond farm activities has been suggested in this paper which will be useful not only to the country but also to the transboundary Himalayan region where trout farming is still rudimentary.
Dietary ingredient composition alters faecal characteristics and waste production in common carp reared in recirculation system
2019, Aquaculture
Citation Excerpt :
Impact of alternate ingredients on the digestibility of nutrients in fish has been reported by many studies. However, information on the impact of ingredient composition of the diet on the chemical composition of faeces is scarce, except for some specific studies focusing on waste management in relation to diet composition (Meriac et al., 2014a, 2014b; Davidson et al., 2013). This experiment showed that, the composition of the faeces strongly varied in carp fed the different diets.
Feed is a common factor influencing both fish growth and waste production in aquaculture. We examined the effect of different feed ingredients on the quantitative and qualitative aspects of faecal waste produced by common carp. Ingredients rich in (i) starch (field peas, PEA); (ii) protein (feather meal, FeM); (iii) insoluble non-starch polysaccharides, NSP (sunflower cake meal, SFM); or (iv) soluble NSP (wheat dried distillers grain with soluble, WDG) were studied. Five experimental diets were produced, a control diet produced from a basal mixture (CON) and four other diets (PEA, FeM, SFM and WDG) were prepared by replacing 30% of the basal mixture in CON with the respective test ingredient (70:30). Common carp juveniles (95 g, 15 fish per tank) were fed (restrictively, 22 g/kg^0.8/d) the experimental diets for 7 weeks, in triplicate groups. Growth, body composition, energy and nutrient balances were significantly different; with highest growth recorded in CON and WDG; lowest in the FeM and SFM groups. Apparent digestibility coefficient (ADC) of dry matter, nutrients (protein, fat, carbohydrate, ash and phosphorus) and energy in the diets and ingredients were significantly altered between the groups (p < .001). PEA had the best ADC for macro-nutrients and energy, while ash and phosphorus were highest with WDG; SFM had the lowest ADC values for DM, fat, carbohydrate, energy, and phosphorus. The quantity, proximate composition and recovery percentage of the feaces (collected by settling) was significantly different between treatments (p < .001). Faeces recovery and solid removal efficiency were the highest in WDG, comparable to CON; and lowest in SFM. Physical characteristics of the feaces (stripped) indicated by dry matter content and stability were significantly affected by the ingredients only at day 26 and 29, respectively. However, changes in dry matter and stability over time (days) were significant in SFM and WDG (for DM); and all groups except SFM (stability). Osmolality and viscosity of the stripped faeces was unaffected. In summary, SFM resulted in significantly lower performance, low DM and nutrient digestibility, increased faecal loss, lower stability and removal efficiency. FeM lowered growth, protein and fat digestibility; with altered faecal chemical composition. WDG and PEA performed on par with control, if not better in certain aspects with respect to mineral availability and faecal recovery. Overall, 30% inclusion of the test ingredients not only affected growth, but also the waste production and removal efficiency by altering the physical and chemical characteristics of the faeces in common carp.
Treatment of aquaculture effluent with Chlorella vulgaris and Tetradesmus obliquus: The effect of pretreatment on microalgae growth and nutrient removal efficiency
2019, Ecological Engineering
Citation Excerpt :
While this has been carried out in aquaculture systems using various external carbon sources (van Rijn et al., 2006; Zhu et al., 2015), their use comes with an additional cost. A possible solution is the use of sludge from the RAS itself as a carbon source and, thus, reduce sludge and nitrate concomitantly (Meriac et al., 2014; Suhr et al., 2014), yet this approach achieves no resource recovery and thus no added value is obtained. Microalgae-based technologies are a promising solution for aquaculture wastewater treatment (Egloff et al., 2018; Gao et al., 2016; Posadas et al., 2015; Van Den Hende et al., 2014a) and the microalgae biomass obtained can be valorised (Barnharst et al., 2018; Guo et al., 2013; Milhazes-Cunha and Otero, 2017).
The ongoing and increasing worldwide demand for fish has caused a steady increase in aquaculture production during the last decades. This emphasizes the importance of farming systems with a low ecological footprint, like recirculating aquaculture systems (RAS), which are an alternative to traditional open systems. Furthermore, implementing microalgae treatments in RAS, sustainable water management and low discharge of concentrated wastewater could be achieved, allowing its reuse in the system. The influence of three factors on microalgae treatment efficiency in RAS water were studied: i) microalgae species (Chlorella vulgaris, Tetradesmus obliquus), ii) water pre-treatment (sterile filtration), and iii) sampling location within the RAS (e.g. from fish tank, after UV-disinfection, etc.). To this end, fully factorial, replicated cultivations were carried out in 100-ml flasks, and nutrient removal, microalgae growth, and density of bacteria and protozoa were measured for up to 18 days. Results show that both species are able to grow in RAS water and effectively remove nutrients in it, yet their performance depended greatly on water quality. In sterile RAS water, growth and nutrient removal efficiency of C. vulgaris surpassed that of T. obliquus. In non-sterile RAS water, the pattern reversed because of grazing protozoa. The location of sampling within the RAS had no discernible effect on microalgae growth or nutrient removal efficiency. The results confirm that a microalgae-based technology to treat and valorise RAS water is technically feasible, yet caution that inferences made can be reversed depending on the choice of the species and the pretreatment of the RAS water prior to cultivation.
Novel tri-bore PVDF hollow fiber membranes for the control of dissolved oxygen in aquaculture water
2019, Journal of Water Process Engineering
Citation Excerpt :
Another method is to convert nitrate through a biological process named as denitrificaiton. Denitrification depends on facultative heterotrophic bacteria which reduces nitrate NO3− to nitrite (NO2−), nitric oxide (NO) and nitrous oxide (N2O), before eventually converted to N2 [2,7,9–12]. Though relatively expensive compared with water replacement, biological denitrification attracts more attention recently because it offers high rate of nitrate removal and minimizes the discharge of wastewater and consumption of new water.
Novel tri-bore hollow fiber membranes have been developed from polyvinylidene fluoride (PVDF) for the control the dissolved oxygen (DO) in aquaculture denitrification process. The fabricated hollow fibers are characterized in terms of morphology, porosity, hydrophobicity and mechanical strength. Two membrane modules, each including 200 pieces of hollow fibers, are connected in series or parallel in order to determine the optimum operation mode. The deoxygenation test is firstly conducted for DI water and then for aquaculture water. Various methods including water flushing, air blowing or chemical cleaning have been applied to assure the cleaning efficiency after membrane fouling. A mathematical model has been developed by using the resistance-in-series concept by taking into account boundary layer and membrane characteristics. Overall mass transfer coefficient, radial and axial concentration profiles, and molar flux of oxygen at different water flow rates are calculated. This work has demonstrated that the developed tri-bore hollow fiber membranes are applicable for the control of dissolved oxygen in aquaculture water. The observations have provided solid evidence for the development of membrane-based denitrification system for recirculating aquaculture system (RAS).
Novel tri-bore PVDF hollow fiber membranes for the control of dissolved oxygen in aquaculture water
2019, Journal of Water Process Engineering
Novel tri-bore hollow fiber membranes have been developed from polyvinylidene fluoride (PVDF) for the control the dissolved oxygen (DO) in aquaculture denitrification process. The fabricated hollow fibers are characterized in terms of morphology, porosity, hydrophobicity and mechanical strength. Two membrane modules, each including 200 pieces of hollow fibers, are connected in series or parallel in order to determine the optimum operation mode. The deoxygenation test is firstly conducted for DI water and then for aquaculture water. Various methods including water flushing, air blowing or chemical cleaning have been applied to assure the cleaning efficiency after membrane fouling. A mathematical model has been developed by using the resistance-in-series concept by taking into account boundary layer and membrane characteristics. Overall mass transfer coefficient, radial and axial concentration profiles, and molar flux of oxygen at different water flow rates are calculated. This work has demonstrated that the developed tri-bore hollow fiber membranes are applicable for the control of dissolved oxygen in aquaculture water. The observations have provided solid evidence for the development of membrane-based denitrification system for recirculating aquaculture system (RAS).

View all citing articles on Scopus

View full text

Denitrification on internal carbon sources in RAS is limited by fibers in fecal waste of rainbow trout

Highlights

Abstract

Introduction

Section snippets

Experimental design

Water quality, fish performance and system management

Water quality and management

Conclusions

Acknowledgments

Bioresour. Technol.

Aquaculture

Aquaculture

Aquaculture

Aquac. Eng.

Aquaculture

Aquac. Eng.

Bioresour. Technol.

Aquaculture

Aquaculture

Aquac. Eng.

J. Anal. Appl. Pyrolysis